I'm doing a multilingual livestream using OBS Studio on Windows 10. OBS can detect and stream these multiple languages, provided they are all available as channels of one audio source. We would then add this source into OBS and go ahead with the stream.

The issue here is that the commentaries in various languages are coming in through different audio sources, for eg. a Scarlett 2i2, 2 channels embedded on the SDI with the video signal etc.

Is there anyway to club these various audio sources into a single "virtual source" with 8 channels, and map each physical source into it? Then I could add this "virtual" source into OBS.

You will be wanting to use a "virtual audio cable" product which allows you to remap inputs to outputs. You may also need a real-time audio mixer in order to process the incoming signals. Reaper may be suitable for this application.